Papermaking machines for dewatering the paper material include a wire part, a press part and a drier part. The wire part, the press part and the drier part are arranged in the order named along the direction in which the wet paper web is transferred.
Some papermaking machines are of the type which transfers the wet paper web in open draws. The open-draw papermaking machines do not support the wet paper web with belts. As a result, the wet paper web tends to be broken in a region in which it is transferred from one section to another. Accordingly, the open-draw papermaking machines are difficult to operate at higher speeds.
In recent years, papermaking machines which are of the type for transferring the wet paper web in closed draws are prevalent in the art. The closed-draw papermaking machines have a belt for transferring the wet paper web. The wet paper web is placed on the belt and transferred by the belt from one section to another. As a result, the closed-draw papermaking machines can operate at higher speeds and more stably.
In the closed-draw papermaking machines, the wet paper web is transferred by being transferred successively through the wire part, the press part and the drier part. In the press part, the wet paper web is transferred by the transfer belt, and pressed by a press to squeeze water out. Thereafter, the wet paper web is dried in the drier part.
The present applicant has proposed, in Japanese published patent application No. 2004-277971, a wet paper web transfer belt which has a first function to cause the wet paper web to stick thereto and transfer the wet paper web and a second function to allow the wet paper web to be smoothly released therefrom for transferring the wet paper web to a next process. The wet paper web transfer belt includes a wet paper web-side layer comprising a high-polymer elastic region and a fibrous body. The fibrous body is hydrophilic and partly exposed on the surface of the wet paper web-side layer.
As the hydrophilic fibrous body, which is exposed on the surface of the wet paper web-side layer, retains the water from the wet paper web, it performs the first function to cause the wet paper web to stick thereto and transfer the wet paper web. The portion of the fibrous body, which is exposed on the surface of the wet paper web-side layer, performs the second function to allow the wet paper web to be smoothly released therefrom for transferring the wet paper web to a next process.
Patent document 1: Japanese published patent application No. 2004-277971
The wet paper web transfer belt disclosed in Japanese published patent application No. 2004-277971 has both of the above two functions balanced. However, when part of the water contained in the wet paper web is absorbed by the hydrophilic fibrous body (e.g., rayon fibers) of the wet paper web-side layer, the fibrous body expands, making the wet paper web transfer belt dimensionally unstable. In recent years, particularly since the wet paper web transfer belt is required to travel at increased speeds, it is necessary to reduce an increase in the widthwise dimension of the belt which is caused by the absorption of water by the hydrophilic fibrous body.
The present invention has been made to solve the above problems. In order to improve the first function to cause the wet paper web to stick thereto and transfer the wet paper web and the second function to allow the wet paper web to be smoothly released therefrom for transferring the wet paper web to a next process, the hydrophilic fibrous body is formed in the wet paper web-side layer of the wet paper web transfer belt by needle punching. It is an object of the present invention to provide a wet paper web transfer belt which is capable of reducing an increase in the widthwise dimension of the belt which is caused by the absorption of water by a hydrophilic fibrous body.